The present invention relates to a quartz glass jig and a method for producing the same; in further detail, it relates to a quartz glass jig free from microcracks and having large irregularities on the surface thereof, and to a method for producing the same.
Conventionally, high purity quartz glass jigs having a relatively high thermal resistance and high chemical resistance are widely used for the production of semiconductor devices. Furthermore, it is often the case that irregularities are intentionally provided on the surface of the jigs, and these irregularities are generally formed by frost treatment. However, a conventional frost treatment comprises shaving off the surface of the quartz glass jigs by spraying a powder of crystalline silicon dioxide. Thus, microcracks generate at the same time irregularities are formed, and this caused selective etching of the microcracks during the subsequent rinsing treatment using an aqueous solution of hydrogen fluoride. This led to problems such as the adhesion of etching solution or to the generation of particles which contaminate the semiconductor products.
As a means to solve the problems above, in JP-A-Hei10-273339 (the term, xe2x80x9cJP-Axe2x80x9d as referred herein signifies xe2x80x9can unexamined published Japanese patent applicationxe2x80x9d) is proposed a quartz glass jig having a rough surface formed by a structure comprising irregular elevations extended between the first upper level and the second lower level, the surface of which having an average height in the range of from 0.1 to 10 xcexcm and protruded portions having an average width in the range of from 30 to 180 xcexcm. In Japanese patent application JP-Hei-9-282757 is proposed a quartz glass jig having spherical or ellipsoidal irregularities on the surface thereof.
When CVD process is carried out by using the former type of quartz glass jig above, however, although thin films free from the generation microcracks and in which the generation of particles is suppressed are obtained in the initial stage, the irregularities on the surface of the jig are lost with repeated rinsing. This was found to cause a problem of forming microcracks on the thus vapor deposited thin film, which led to the generation of particles that contaminate the semiconductor products. Thus quartz glass jigs should be obtained capable of realizing thin films deposited by CVD process free from the formation of microcracks even after repeated rinsing and free from the generation of microcracks, thereby capable of obtaining semiconductor products free from contamination. The present invention has been accomplished based on these findings.
Thus, an object of the present invention is to provide a quartz glass jig having large irregularities on the surface thereof.
Furthermore, another object of the present invention is to provide a quartz glass jig which realizes an oxidation film formed by CVD process and the like free from the formation of microcracks even after repeated rinsing, and which is also free from causing contamination of semiconductor products attributed to the generation of particles.
Yet further object of the present invention is to provide a simple method for producing the quartz glass jig above.
Accordingly, the present inventors have intensively conducted studies to solve the problems above. The present invention which accomplishes the objects above provides a quartz glass jig having large irregularities on the surface thereof, characterized in that said irregularities have a center line roughness Ra in the range of from 2 to 30 xcexcm, a maximum height Rmax in the range of from 10 to 150 xcexcm, and a width in the range of from 10 to 500 xcexcm on the surface of the quartz glass jig, and a method for producing the same, which comprises repeating several times a process of forming an inorganic thin film on the surface of a quartz glass jig free from microcracks and having fine irregularities on the surface thereof, and thereafter rinsing it.
The quartz glass jig according to the present invention is useful as a jig for use in the semiconductor industry, for example, a furnace core tube, a boat for mounting wafers thereon, etc. The quartz glass jig is free from microcracks, and which comprises a surface on which irregularities are partly or entirely formed with a center line roughness Ra in the range of from 2 to 30 xcexcw, preferably, from 10 to 30 xcexcm, a maximum height Rmax in the range of from 10 to 150 xcexcm, preferably, from 50 to 150 xcexcm, and a width in the range of from 10 to 500 xcexcm. Because the quartz glass jig comprises such large irregularities and is free from microcracks, there is no change in surface roughness even after an etching treatment using a 5% hydrofluoric acid, and it maintains the irregularities without change in center line roughness and in the maximum height. Accordingly, even if these quartz glass jigs are used in CVD processes and are subjected to repeated rinsing, the oxide films formed thereon remain free from microcracks and do not contaminate semiconductor products attributed to the generation of particles. Particularly preferred is, as shown in FIG. 1, that the irregularities are formed from a plurality of slopes, and the apex at which the slopes cross with each other forms an edge line, for example, the irregularities are formed in a shape similar to the roofs such as a gable roof or a hip roof. The slopes above may be planar or curved planes. The term xe2x80x9crinsingxe2x80x9d as referred herein signifies rinsing using an aqueous hydrofluoric add solution, or a mixed solution of hydrofluoric acid with an inorganic acid such as nitric acid or sulfuric acid. If the irregularities have a center line roughness Ra of lower than 2 xcexcm, the thin film is subject to the generation of microcracks, and if the irregularities yield a center line roughness Ra exceeding 30 xcexcm, it becomes difficult to form large irregularities. Similar to the case of center line roughness Ra, irregularities having a maximum Rmax or a width falling out of the aforementioned ranges cannot form a favorable quartz glass jig.
Futhermore, it has been found that the quartz glass jig having large irregularities on the surface thereof can easisy be produced by repeating the steps of forming an inorganic thin film on the surface of a quartz glass jig free from microcracks but having fine irregularities, followed by rinsing.
The quart glass jig having large irregularities on the surface thereof can be produced by first forming a thin film of silicone and the like in accordance with, for instance, the description given in the specification of Japanese patent application JP-Hei-9-282757, and then subjecting the resulting product to an etching treatment using an aqueous solution of hydrofluoric acid, or by immersing the quartz glass jig into a solution consisting of a mixture of hydrofluoric acid, ammonium fluoride, and acetic acid in accordance with the frost treatment as described in JP-A-Hei10-273339, thereby forming fine irregularities free from microcracks on the surface by using the precipitates of ammonium silicofluoride, and then repeating at least twice a step of coating the surface of the jig with an inorganic thin film followed by rinsing until there is formed irregularities having a center line roughness Ra in a range of 2 to 30 xcexcm, preferably, in a range of 10 to 30 xcexcm, a maximum height Rmax in a range of 10 to 150 xcexcm, preferably, in a range of 50 to 150 xcexcm, and a width in a range of 10 to 500 xcexcm. Unlike the case of a conventional sandblasting method, in which microcracks are generated and in which aqueous hydrofluoric acid intrudes into the microcracks to form acute front ends due to the release thereof into oval shapes, the above method of forming irregularities comprising coating an inorganic thin film and rinsing, the apices of the irregularities are formed in the shape of smooth slopes. As the inorganic thin films above, there can be mentioned thin films of at least one type of material selected from silicon compounds, silicon nitride compounds, silicon oxide compounds, and silica glasses. The reason why large irregularities are formed by thus rinsing after forming an inorganic thin film on the surface of a quartz glass having fine irregularities and free from microcracks is that, presumably, visually non-discernible fine microcracks are formed at the time the thin film is formed on the indented portions of the fine irregularities, and the rinsing solution intrudes along the fine microcracks as to selectively etch and enlarge the irregularities, The inorganic thin film is preferably formed in a range of from 0.1 to 100 xcexcm. If the thin film is formed at a thickness less than 0.1 xcexcm, there is no increase in roughness nor formation of large irregularities on rinsing. If the thin film is formed at a thickness exceeding 100 xcexcm, visually observable linear microcracks form, and these microcracks reach to the quartz glass jig and develop in such a manner to surround the quartz glass jig. Thus, it is not preferred because quartz glass tends to fall off.